Sagan et al.1 have suggested that the cumulative impact of anthropogenic albedo changes may have contributed to global climate changes in the past and that its effect may be continuing. Using a statistical dynamic climate model (SDM) with more realistic surface albedo changes than previously used2, we have computed the combined impact of desertification of the Sahara and deforestation of the tropical rain forest. While the model computed a surface cooling of 0.6 K for the Northern Hemisphere, the global mean of ~0.2 K was substantially less than the 1 K suggested by Sagan et al.1. We infer that man's cumulative impact on planetary surface albedo over the past few thousand years has had a small and probably undetectable effect on global climate.